Abstract: A phase-locked loop (PLL) frequency synthesizer having an analog, out-of-band component path and a digital, in-band component path to provide frequency modulation (FM) of the synthesized output signal is described. The in-band FM component is octave scaled by an analog scaling means and coupled to an analog-to-digital converter to provide a digital number to be decade added to the PLL divide number to change the PLL frequency in response to the in-band FM signal. The out-of-band FM component is also scaled and applied to a loop summing node and summed with the PLL error signal to vary the PLL frequency. The scaling in both the in-band component path and out-of-band component path is equalized to provide a flat frequency response. Additional, the in-band component is scaled to allow use of the analog-to-digital converter over its maximum range to maintain a high signal-to-noise ratio.

Abstract: A four-channel multifunction digital frequency synthesizer which uses direct numerical synthesis to generate one or more complex output signals having selectable frequency, phase offset, amplitude level and waveform is provided. A waveform synthesizer digitally synthesizes precise sine, square, triangle, ramp, uniform and Gaussian noise and DC waveforms which can be selected for any of the four channels. One of the four channels can be frequency, phase and amplitude modulated by the signals on the remaining three channels in any combination. The four channels are time-multiplexed which allows the use of a single frequency synthesizer to realize four independent channels and a large number of support functions and capabilities in a high-density VLSI integrated circuit on a single chip. The synthesizer system can provide up to four independent output signals which can be any one of the four channel signals, or any combination of the four channel signals summed to form a complex waveform signal.